The method for treating congenital heart diseases by transcatheter intervention has been widely accepted at present. In comparison to the conventional surgical therapy, the method has obvious advantages, mainly embodies in less trauma and fast recovery.
For example, the principle of treating Atrial Septal Defect (ASD) by transcatheter intervention is as follows: an elastic occlusion instrument is compressed into a small-size or a narrow and long shape and then conveyed to a defect position through a conduit, and then the elastic occlusion instrument is self-expanded to a preset shape, where the preset shape often includes two disks and a connecting component connecting the two disks. The two disks are disposed on two sides of the defect to occlude the defect. Such occlusion instrument is often called an occluder or an occlusion device.
Early disk is made from highly rigid metal. In a heart, such disk will bear cyclic stress action caused by heartbeat, so many occlusion instruments will be fractured due to fatigue stress.
An occlusion device braided from a plurality of fine metal wires (hereinafter referred to as a braided occlusion device) has been developed. On one hand, as the braiding strands are fine and flexible and generate a small stress due to deformation along with heartbeat, the ability to resist fatigue fracture is obviously improved; on the other hand, in such occlusion devices formed by a plurality of braiding strands, even though a few strands are cracked, the crack does not easily spread to other portions of the disk, so the whole device has good fatigue resistance. Although there still are some disadvantages, such a braided occlusion device has a good clinical manifestation as a whole when applied in the occlusion of Atrial Septal Defect (ASD). However, when a similar design is applied in the occlusion of Patent Foramen Ovale (PFO), new disadvantages are manifested. A main distinction between the atrial septal defect and the patent foramen ovale in the physiological structure lies in that the atrial septal defect looks like an obvious gap or a porous structure in shape, while the patent foramen ovale looks more like a channel having an overlapped portion. Due to this characteristic, occlusion devices for occluding patent foramen ovale require a more flexible connecting structure.
FIG. 1 is a cross-sectional diagram of four chambers of a heart. The channel of PFO is located between a right atrium 11 and a left atrium 12, and an occlusion device is placed at this position. The anatomical structure of patent foramen ovale differs from that of a common atrial septal defect. The patent foramen ovale looks more like a narrow and long channel than a porous defect, and a septum secundum 1 and a septum primum 2 between the left atrium and the right atrium are partially overlapped. For most people, after growth and development, at the overlapped position of the septum secundum 1 and the septum primum 2, both will be merged as one so as to separate the left atrium from the right atrium. If the overlapped portion fails to be merged, a channel communicating the left atrium and the right atrium is formed, and this channel is called patent foramen ovale. Due to a large individual difference, the anatomical structure near the patent foramen ovale is mainly embodied in the difference in thickness of an atrial spectrum, for example, the thickness of the septum secundum 1. In some individuals, the average thickness of the septum secundum 1 may be 2 mm; while in other individuals, the average thickness of the septum secundum 1 may be 8 mm.
The common occlusion method for patent foramen ovale is to implant an occlusion device having two disk-shaped structures (hereinafter referred to as disks), as disclosed in CN0719448.1. In the double-disk occlusion device 3 in FIG. 1, a first disk 31 and a second disk 32 tightly holds two atrial spectra (including a septum secundum 1 and a septum primum 2) which are not completely fitted, and then the two disks are connected via a waist connecting structure 33 (hereinafter referred to as a waist) so as to fit the atrial spectra. After the occlusion device is implanted, endothelium will grow gradually and finally wrap the whole double-disk occlusion device 3 until a radical occlusion is formed.
In ideal conditions, after an occlusion device is implanted, the first disk 31 and the second disk 32, which are disposed on two sides of PFO, respectively, are closely clung to walls on two sides of the atrial spectra. In an atrium, a portion of the disk closely clung to the atrial wall is easily and quickly covered by endothelial cells, while a protrusion portion 34 on the first disk and a protrusion portion 35 on the second disk take more time to be covered, and often still are exposed in blood after other portions are completely covered by endothelium. As foreign matters, the protrusion portions exposed in blood will cause a rejection reaction of the human body and thus are an important inducement of the formation of inflammation and thrombus. Before the occlusion device is not completely covered by endothelial cells, a patient needs to continuously take anticoagulants, or there may be a risk of locally forming thrombus. The thrombus formed in the left atrium 12 may directly enter systemic circulation after falling off, so that it is likely to result in dangerous diseases such as apoplexia or acute myocardial infarction. Therefore, the disk of an occlusion device, especially a disk 31 placed in the left atrium 12, should have a flat structural characteristic and have no protrusion on the disk surface, most preferably a single-layer braided disk-shaped structure (hereinafter referred to as a single-layer disk). In comparison to the left atrium, when the second disk 32 in the right atrium 11 generates thrombus in the right atrium, the dangerous level of the thrombus will be far lower than that of the thrombus in the left atrium. Small thrombus will not cause an obvious danger or symptom after reaching the lung, while large thrombus will be likely to cause obvious damage to the lung. Therefore, the second disk 32 placed in the right atrium may be a double-layer fabric braided disk (a double-layer disk for short) in the prior art. In the double-layer disk in the prior art, a structure for connecting a conveying system is often provided on an outer side (a side away from the waist 33) of the disk. This structure will often from a protrusion portion 35 on the second disk 32. However, in the right atrium, it is widely believed that this is acceptable.
In addition, different individuals have different thicknesses of atrial spectra. Typically, the thickness of the upper side is larger, while the thickness of the lower side is smaller. As shown in FIG. 1, the thickness of the septum secundum 1 is obviously larger than that of the septum primum 2. This requires that the occlusion device have a flexible waist 33 which may allow the first disk 31 and the second disk 32 to relatively deflect at a certain angle and simultaneously allow a relative offset between the two disks in a section direction of the disks. If improvements are made to the prior art, the flexible waist 33 may improve the compliance of the whole occlusion device, so that it is advantageous for the fitting of the two disks to the walls of atrial spectra. The fine waist 33 occupies a smaller space, so it is advantageous for the fitting of two atrial spectra 1 and 2. If the rigidity of the waist of the occlusion device is high, the positions and angles of the two disks cannot be flexibly adjusted relative to each other. As a result, possibly, only one portion of a certain disk is fitted with the atrial spectra, while both inner and outer sides of the other portion of disk are exposed in blood. For example, in FIG. 1, if the first disk 31 and the second disk 32 cannot form a certain angle and thus are parallel to each other, a lower edge 37 of the first disk 31 cannot be closely clung to the atrial spectrum 2 or a lower edge 36 of the second sick 32 cannot be closely clung to the atrial spectrum 2. However, this portion separated from the atrial spectrum is often difficult to be covered by endothelium, resulting in the delay of endothelialization. Therefore, it is required to prolong the time of taking anticoagulants, and the local hemodynamics is thus influenced. Once the anticoagulants are stopped in the case of incomplete endothelialization, the risk of inducing thrombus is caused. If the placement of an occlusion device has a relatively obvious offset, the inner sides of two disks will be partially separated from the atrial spectra, thereby resulting in a higher thrombus risk. As can be seen, the flexible waist 33 may improve the overall performance of the occlusion device and reduces postoperative risks.
In the prior art, many braided occlusion devices do not have the two important features of a flat single-layer disk and a flexible waist. Occlusion devices braided from a plurality of braiding strands in the prior art will be briefly described below.
CN97194488.1 discloses an occlusion device, for example, a double-disk occlusion device 3 in FIG. 1. The occlusion device includes a support fabric having contractility. The support fabric constitutes a main body structure of the device, and a first disk 31 and a second disk 32 included in the main body structure and a waist 33 form an integral braided structure. One end of the braiding strands of the support fabric form the first disk 31, the middle portions of the braiding strands are gathered to form the waist 33, and the other ends of the braiding strands form the second disk 32. Both disks are of a double-layer braided structure. In order to achieve a practical occlusion effect, tens of elastic braiding strands are often required to weave the support fabric. As all the braiding strands densely pass through the waist 33, the waist has a high rigidity and is difficult to bend. Thus, the adjustable range of an angle between the two disks is very small, a relative offset cannot be realized along a disk surface direction, so that the two disks cannot better adapt to different anatomical structures and it is likely to result in insufficient fitting of disks and walls. Meanwhile, on the outer side of the first disk 31 of the occlusion device placed in the left atrium, the ends of the braiding strands are gathered and secured together to form a protrusion portion 34 on the first disk 31, so that the flat characteristic of the double-layer disk on one side of the left atrium is damaged. This protrusion portion 34 is often takes more time to achieve endothelialization than other portions and is even likely to be not completely endothelialized after the occlusion device has been implanted for several years. Typically, the patient undergoing this implantation operation will only take anticoagulants for half a year. Without anticoagulants, the non-endothelialized protrusion portion is likely to induce the formation of thrombus. In the article titled A late complication of a patent foramen ovale amplatzer occlusion device, Mohaned Egred, et al described an example in which thrombus was adhered onto the protrusion portion of the occlusion device after the occlusion device was implanted for many years.
The occlusion device disclosed by CN200780010436.7 may be regarded as an improvement on the basis of CN97194488.1. Their differences lie in that all tail ends of the braiding strands of the occlusion device disclosed in the former Chinese patent application are secured within a protrusion on the second disk 2, while there is no protrusion for securing the braiding strands on the first disk 31. That is, there is no convex structure protruding from the disk surface. The flat characteristic of the first disk 31 is improved. However, all the braiding strands of the occlusion device pass through the waist 33 twice, so the waist 33 has a higher rigidity and is difficult to bend.
The two occlusion devices described above in the prior art have a common feature that they are of an integral structure braided from braiding strands. A portion of a same braiding strand forms a first disk, another portion thereof forms a second disk, and a third portion thereof forms a waist. Such a design will certainly result in high rigidity of the waist. In the prior art, there also are split type occlusion devices braided from a plurality of braiding strands. These occlusion devices are characterized in that the braiding strands forming the first disk separately form this disk, but will not pass through the waist and participate in forming the second disk, the material of the waist is radically reduced, and this makes the optimization of the waist possible. However, in the prior art, the known occlusion device of a split type structure cannot have the features of a flat single-layer disk and a flexible waist connecting structure at the same time either.
US20040143291A1 discloses an occlusion device having a center post feature. This occlusion device includes two single-layer disks, each being constructed of a plurality of radially-arranged support rods and flexible occlusion device sheets adhered to the support rods, the support rods being braided from a plurality of braiding strands; and the two single-layer disks are connected by a center post having joints. A plurality of radial holes, through which the support rods constructing the single-layer disks are passed, are alternately arranged in the axial direction at two ends of the center post. The support rods on the single-layer disks are passed through different radial holes on the center post, to form a criss-cross arrangement. The thickness of the single-layer disk at the edge is equal to the diameter of the support rod. The thickness of the single-layer disk in its center is equal to the sum of diameters of the plurality of support rods. For example, when a single-layer disk is constructed of three support rods, the thickness of the single-layer disk in the center is at least equal to the sum of the diameters of the three support rods. Such a single-layer disk is lack of excellent flatness. However, in the absence of the center post, the support rods on a same single-layer disk are loosened, and cannot form an independent and stable disk-shaped structure. The center post of this occlusion device plays a role of, on one hand, connecting the two single-layer disks to form a waist, and on the other hand, restricting the support rods on the single-layer disks so that the single-layer disks form a stable disk-shaped structure. The center post is formed by connecting three rigid structures together in a manner as for joints, and is thus poor in flexibility. Furthermore, the tail end of the center post will protrude out of the outer side of the single-layer disk. Further improvement is required.
In conclusion, the braided occlusion devices in the prior art, regardless of one-piece structures or split-type structures, fail to have two important features simultaneously, i.e., flat single-layer disks and a flexible waist. For one-piece occlusion devices in the prior art, all braiding strands forming the first disk are passed through the waist to the second disk. As a result, the rigidity of the waist is absolutely too large due to intensive material in the waist. The ends of the braiding strands are intensively fixed to one or two points and those points often form a protrusion structure on the disk, and consequently, the flatness feature of the disk is damaged. For split-type occlusion devices in the prior art, the braiding strands are braided into a plurality of support rods first and the support rods are then connected to the center post to form an occlusion device. In the center of the disk where the support rods are overlapped, the thickness is significantly greater than the thickness of the edge, so that the flatness feature of the disk is damaged. In order to fix a plurality of separated support rods, the part of the center post, to which the supports are connected, requires a sufficient rigidity to restrict the location and direction of each of the support rods. This restricts the flexibility of the center post. As a result, the deformation part of the center post occurs at the joints, and self-adaptive deformation according to the particularly physiological structure of a patient is impossible.